Where does security fit in bi-modal IT departments?

When restructuring an IT department, the recent trend has been to look at possibly breaking it into two factions. One group that handles the daily tasks by putting out fires, and one that looks ahead in trying to create a new landscape that is immune to those fires.
The bi-modal idea has its benefits and its pitfalls but the determination seems to come down to the size of the enterprise. In the mid to smaller companies, there is not the luxury of splitting the security group out into subgroups.